The present invention relates to an elevator system. More particularly, the invention relates to a traction elevator system including a guide axis aligned with a traction member.
Traction elevator systems commonly include one or more guide rails running vertically on opposite sides of a hoistway. The guide rails commonly have a T-shaped horizontal cross-section with the top of the T attached to the side of the hoistway and the leg of the T extending into the hoistway toward the elevator car. The guide rails are arranged to guide the elevator car up and down the hoistway. Some traction systems may include a car frame attached to the elevator car. In systems including a car frame, the frame is attached to the car and connected to the guide rails such that the car frame, which rides vertically on the rails, carries the car up and down the hoistway. The connection at the guide rails, either between the car and the guide rails or between the car frame and the guide rails, commonly includes one or more guides, such as rollers or slides, which provide a sliding connection to the guide rails and often include damping devices to improve the ride quality of the elevator car. Some traction elevator systems also include sheaves provided above the car in, for example, a front to back arrangement along the sides of the car adjacent to the guide rails. Traction members, such as belts or ropes, loop around the sheaves and transmit force provided by a drive system, commonly called a hoist machine, to move the elevator car, and in some systems the car frame, up and down the hoistway along the guide rails.
Two important design considerations for elevator systems are the weight capacity, sometimes referred to as the duty, of the car and the ride quality of the car. The duty of the elevator car in traction systems depends upon the roping ratio (e.g., 2:1 or 3:1) as well as the number of traction members, for example belts, used to drive the car, and in some cases the car and the car frame. For example, for a given roping ratio, the duty of an elevator car driven by five traction belts is greater than the duty of an elevator car driven by four similar traction belts. Additionally, the ride quality of the elevator car may be related, in part, to the relative position of the traction belts with respect to the car and the path along which the car travels, i.e. the path along the guide rails.
In some traction elevator systems in which the sheaves are provided in a front-to-back arrangement along the sides of the top of the car frame, the traction members that engage the sheaves are arranged such that they do not interfere with the guides' interactions with the guide rails. Unfortunately, as a result of the guides' position relative to various traction members, the possibility of providing an additional traction member(s) in the location occupied by the guides is precluded, thereby reducing the duty that the car may otherwise be capable of lifting. Additionally, the position of the guides may prevent aligning one of the traction members with the guide and guide rails, thereby reducing the ride quality of the car.
In light of the foregoing, the present invention aims to resolve one or more of the aforementioned issues that afflict such traction elevator systems.